1. Technical Field
This invention relates generally to image capture devices having automatic focus capabilities, and more particularly to an image capture device having an electronically controllable focal length adjustment device used for resolving image focus.
2. Background Art
Image capture devices, such as digital cameras, often include an automatic focus feature. This feature allows a user to simply “point and shoot” an image without having to manually focus the camera by physically manipulating a lens element. Conventional “autofocus” cameras generally focus on images by operating a small motor that moves a lens closer to or farther away from an image sensor.
Conventional autofocus features come in two forms: active and passive. In active systems, the camera will send a beacon—such as an infrared or sonic beam—that bounces off an object. Based upon the time delay in receiving the return signal, the camera guesses how far away the object is and moves the lens an appropriate distance away from the image sensor to achieve a reasonably well-focused image. In passive systems, a microprocessor analyzes high frequency components of an image seen by an image sensor and adjusts the distance of the lens relative to the image sensor until a maximum intensity difference between adjacent pixels (sometimes referred to as contrast) is obtained, which is indicative of optimal focus.
Conventional autofocus systems are problematic for modern, small, portable electronic devices such as mobile telephones or handheld computers. First, they are mechanical in nature, requiring substantial space for many moving parts. In small, handheld devices, there is often insufficient space for the motors, lens motion assemblies, and other components that are required. Second, traditional systems employing active autofocus systems require a relatively greater amount of processing power, and correspondingly a general increase power consumption. Passive systems generally have relatively reduced focus ranges, and are generally more greatly impacted at the end of the focus range associated with the resolutions of near-field images. Further, passive systems may generate image “artifacts” or aliasing that compromise the overall integrity of the image.
There is thus a need for an improved focusing system for image capture devices, including handheld electronic devices such as mobile telephones and computers.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.